This invention relates to a roof structure for a building including a vertically extending essentially non-load supporting central column which is spaced above supporting structure for the roof structure, and at least three trusses joined on their inner ends to the column and extending radially outwardly and downwardly to the roof supporting structure. Each of the trusses is rotationally displaced in a horizontal plane from adjacent ones of the trusses to form at least three triangularly shaped roof segments of a cone shaped polygon configuration.
Broadly speaking, cone shaped polygon roof structures are known in the prior art. See, for example, the gazebo roof disclosed in U.S. Pat. No. 4,739,594 granted to J. D. Langford et al. on Apr. 26, 1988 and the roof structure taught in U.S. Pat. No. 4,332,116 granted to H. A. Buchanan on Jun. 1, 1982. The gazebo roof structure of Langford et al. is made of eight triangularly shaped segments, each segment having two wood side beams of one inch by four inch board joined together at an apex and a series of radially spaced apart cross members. The side beams of the eight segments have inner ends which are mounted in U-shaped brackets secured around a central hub. The roof structure of Buchanan contains fifteen triangularly shaped segments, each segment having two side beams or roof components meeting at an apex, and a series of radially spaced apart cross members. The roof components are supported on their radially inner ends on a support plate which is welded to an upper end portion of a weight supporting central column which extends from floor to ceiling in the reference structure.
None of the prior art roof structures are formed using multi-element truss members. While the gazebo roof structure of Langford et al. contains a non load supporting central hub, the fact that rafters or wood side beams are used severely limits the roof span and, consequently, limits the amount of floor space obtainable under roof. On the other hand, the much greater span of roof structure envisioned by Buchanan requires that his rafters must be supported not only on their radially outer ends by posts or columns, but also by a load supporting floor to ceiling central column in the center of the span.
In the gazebo of Langford et al., adjacent ones of the reference roof supporting posts must be rigidly tied together by cross members to prevent the roof structure from sagging and, thereby, tilt the posts radially outwardly. This would have the effect of spreading the posts apart at their upper ends, therefore permitting the roof to sag and, ultimately, the building to collapse. The cross members thus prevent the upper ends of the posts from spreading apart and therefore prevent the roof from sagging.
It would be desirable to have a cone shaped polygon roof structure of the size envisioned by Buchanan which can be entirely supported on and around an outer perimeter portion of the structure without need for a span interrupting central weight supporting column and without need for rigidly connecting upper ends of adjacent roof supporting posts together to prevent roof sag.
By means of the present invention, these and other problems encountered in such prior art roof structures are substantially eliminated.